This invention generally relates to systems and methods for remotely detecting a volcanic plume using received radiofrequency (RF) signals that have traversed the plume. In particular, this invention relates to systems and methods for remotely detecting a volcanic plume embedded in clouds using satellite-transmitted RF signals.
As used herein, the term “volcanic plume” means a cloud of volcanic ash and the term “volcanic gases” means gases given off by active volcanoes. Dispersed volcanic gases disposed outside the volume occupied by a volcanic ash cloud are not included as part of the “volcanic plume,” as the latter term is used herein.
Volcanic ash can pose a hazard to flying jet aircraft, threaten the health of people and livestock, damage electronics and machinery, and interrupt power generation and telecommunications. Volcanic ash comprises tiny jagged particles of rock and natural glass blasted into the air by a volcano. Wind can carry ash thousands of miles, affecting far greater areas than other volcano hazards.
Volcanic plumes present two problems for aircraft: (a) engine shutdown due to ash; and (b) aircraft damage and/or crew and passenger injury due to ash and corrosive gases. Volcanic ash particles are extremely abrasive. They are jagged particles of rock and glass that can cause rapid wear to the internal workings of jet engines. More important, high temperatures in some parts of jet engines can melt the ash; it then re-solidifies on cooler parts of the engine, forming a layer that blocks airflow, interferes with moving parts, and eventually shuts down the engine.
Another issue is the potentially harmful effects of elevated concentrations of SO2 and sulfate aerosol in ash-poor clouds on aircraft and avionics. In addition, volcanic ash particles, with sulfuric acid adhered thereto, are tiny enough to travel deep into the lungs of human beings, which may be harmful and potentially fatal to people.
Various known solutions for detecting and avoiding a volcanic plume during flight of an aircraft have certain disadvantages. First, in daytime clear weather, pilots can see and avoid the visually distinctive cloud from an erupting volcano. However, volcanic plumes are often encountered during nighttime and/or embedded within other clouds. Therefore, visual detection is not always effective.
Second, for volcanoes that are well monitored, sensors or people on the ground can quickly observe an eruption and report it to flight safety authorities such as the FAA. In these cases, a notice to airmen is issued. However, many remote volcanoes around the world are still not well instrumented and can erupt without immediate detection. Even after detection, the mechanism to issue a notice to airmen imposes a delay for processing and distribution, during which an unwarned aircraft may encounter the plume.
Third, a few satellites are capable of detecting volcanic plumes from orbit, based on the sulfur dioxide spectra, the thermal infrared emission, visible ash clouds, or a combination of these. When a satellite detects a volcanic plume, a notice to airmen is issued. However, satellite observations are not continuous. An eruption that occurs between satellite passes may go undetected for 6 to 12 hours, which is more than enough time for aircraft to encounter the plume. The period of non-detection may go on longer for small eruptions or during overcast conditions. Even after detection, the mechanism to issue a notice to airmen imposes a delay for processing and distribution, during which an unwarned aircraft may encounter the plume.
Fourth, onboard systems for detecting the presence of a volcanic plume during flight have been proposed in various patents. For example, U.S. Pat. No. 5,654,700, entitled “Detection System for Use in an Aircraft,” proposes a system that would detect a volcanic ash cloud ahead of an aircraft by monitoring infrared radiation that traverses the ash cloud; and U.S. Pat. No. 7,383,131, entitled “Airborne Volcanic Ash Cloud and Eruption Detection System and Method,” proposes the provision of an onboard computer having program logic “configured to correlate the location of a volcano from [a] database with the presence of lightning from [a] lightning detector and a volcanic ash plume from [a] weather radar.”
There exists a need for a system that will detect and alert an aircraft to avoid volcanic plumes, which may stretch for hundreds of miles through a variety of atmospheric conditions, including clouds. Detecting plumes embedded in clouds is of particular interest, since these cannot be visually detected by pilots. Repeated fly-throughs of even dilute plumes can cause long-term damage to aircraft, including structures, engines and electrical equipment, because of the corrosive nature of the hydrogen sulfide (H2S) and sulfur dioxide (SO2) gases in plumes.